Question of the Week

Do people moult seasonally?

Sun, 15th Mar 2009

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Question

John, Hong Kong asked:

Do humans moult like other hairy animals such as cats and dogs? In other words, does our hair get thicker in winter while we moult in the summer? If we don't moult, did we once have this function and have we since lost it through evolution?

 

Answer

We put this to Des Tobin, Associate Dean for Research at the School of Life Sciences, University of Bradford:

Kodiak, a 13-year-old captive North American wolf at the UK Wolf Conservation Trust in Berkshire, England.For most animals, like rodents you have a clear-cut wave of hair growth where all the follicles are synchronised. Moulting requires synchronicity in the follicles because the hair grows in a cycle of growth that we call anagen and a resorbative phase called catagen. In the human there is quite a bit of synchronicity in the very early stages: before birth and in the neonatal phase but it breaks up very quickly so that you get what we call a mosaic form of hair growth. Each follicle is an autonomous mini organ. Whilst, to some extent that can be re-synchronised, for example, when women are pregnant because they change their hormonal stimulus. Some studies have been done way back on hair on the thigh. I don't know why they chose thigh hair to check the seasonality of hair but it was shown that in certain times of the year perhaps a little bit related to weather (although with humans you have to be very careful because of the fact that we're wearing clothes for a very long time and we don't need it for the same thermo-regulation that mammals would have) but there is some kind of very minor peaks. If we were to do hair counts we tend to see more shedding as we go into the summer period than going into the winter period.

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We moult continuously. Our hair grows and falls out in cycles.


Not all these follicles are actively growing hairs at any one time. From the moment when it is first formed, each follicle undergoes repeated cycles of active growth and rest. The length of the cycle varies with the individual, and also with the part of the body on which the hair is growing.

http://www.pg.com/science/haircare/hair_twh_23.htm JnA, Tue, 10th Mar 2009

i assume it does to some degree just based on the fact some people's hair will actually become lighter or dark based on the weather season. tony6789, Tue, 10th Mar 2009

But moulting is more of a synchronised process; the hair loss we experience is more stochastic and involves random follicles at any time. Moulting presumably involves multiple simultaneous follicle-down...? chris, Tue, 10th Mar 2009



is that not due more to the light source/ exposure to sunlight? JnA, Wed, 11th Mar 2009



is that not due more to the light source/ exposure to sunlight?



yea, but im guessing that because the seasons cause this change in sunlight exposure it may also trigger hair loss/hair growth? i cud b wrong im just thinking out loud tony6789, Wed, 11th Mar 2009

Isn't 80% of the dust in our homes dead skin cells? If so, then of course we molt our skin... or at least in some way...

Emilio Emilio Romero, Wed, 11th Mar 2009



JnA - do you mean "sloughing", pronounced "sluffing"?


http://www.thefreedictionary.com/Sloughing

slough 2  (slf)
n.
1. The dead outer skin shed by a reptile or amphibian.
2. Medicine A layer or mass of dead tissue separated from surrounding living tissue, as in a wound, sore, or inflammation.
3. An outer layer or covering that is shed.
v. sloughed, slough·ing, sloughs
v.intr.
1. To be cast off or shed; come off: The snake's skin sloughs off.
2. To shed a slough.
3. Medicine To separate from surrounding living tissue. Used of dead tissue. dentstudent, Thu, 12th Mar 2009



JnA - do you mean "sloughing", pronounced "sluffing"?


http://www.thefreedictionary.com/Sloughing

slough 2  (slf)
n.
1. The dead outer skin shed by a reptile or amphibian.
2. Medicine A layer or mass of dead tissue separated from surrounding living tissue, as in a wound, sore, or inflammation.
3. An outer layer or covering that is shed.
v. sloughed, slough·ing, sloughs
v.intr.
1. To be cast off or shed; come off: The snake's skin sloughs off.
2. To shed a slough.
3. Medicine To separate from surrounding living tissue. Used of dead tissue.




um.. another glass of wine anyone?  :) JnA, Thu, 12th Mar 2009

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